Simplify the following expression: $a = \dfrac{-5}{8z} - \dfrac{-9}{8z}$
Answer: Since the expressions have the same denominator we simply combine the numerators: $a = \dfrac{-5 - (-9)}{8z}$ Combine like terms: $a = \dfrac{4}{8z}$ Simplify by dividing numerator and denominator by 4: $a = \dfrac{1}{2z}$